XXV International Mineral Processing Congress (IMPC 2010) Eco-Efficient Gravity Separation Solutions in India

Transcription

1 XXV International Mineral Processing Congress (IMPC 2010) Eco-Efficient Gravity Separation Solutions in India Carlos A. Pena Reference Number: 441 Contact Author: Full name Carlos A. Pena Position title Business Development Manager Organisation Name Mineral Technologies Address 11 Elysium Rd, Carrara, Qld, 4211 Phone Fax Mobile

2 Eco-Efficient Gravity Separation Solutions in India Carlos Pena 1 1. Business Development Manager, Mineral Technologies, 11 Elysium Road, Carrara QLD 4216, Carlos.pena@downeredimining.com

3 ABSTRACT Sustainable development and social responsibility issues are a principal aspect of mineral processing operations around the world. With the need for more environmentally effective technologies, some gravity separation systems have provided eco-efficient mineral processing solutions in places where it is not otherwise viable because of lack of fresh water or for other environmental reasons. Advanced spiral separation technologies developed in Australia offer a cost effective and environmentally viable way to process minerals. In particular, we review recent case studies of spiral plants commissioned in India where environmentally sustainable solutions to design problems included the use of spirals operated with sea water and the use of high capacity (HC) spirals to provide low consumption of energy and materials and a reduced plant footprint. This paper evaluates the performance of various spiral plants in India and how critical environmental issues which affect the overall viability of wet concentrating processes where resolved. Keywords: Spiral separators, Gravity Concentration, Sea water mineral processing INTRODUCTION India is home to a myriad of metals and minerals. Globally, the country is the largest producer of sheet mica, the third largest producer of coal, the fourth largest producer of iron ore, the fifth largest producer of bauxite and one of the largest producers of mineral sands in the world. India s mining industry continues to grow in economic importance. A report from Business Monitor International, noted that India has significant amounts of natural resources, which should allow it to develop a world-class mining industry. The country clearly has massive potential but at present there are a host of problems to overcome, including poor levels of resource recovery, sluggish geological exploration and environmental damage from mining and mineral processing. India having 18% of the world's population on 2.4% of world's total area has greatly increased the pressure on its natural resources. Water shortages, soil exhaustion and erosion, deforestation, air and water pollution afflicts many areas. In fact, India is at risk of severe environmental problems. Many of its rivers are heavily polluted and fresh water sources limited, raising questions about the sustainability of the mining sectors rapid growth.

4 In February 2009, the 20th National Convention of Mining Engineers in India emphasized the importance of clean mining technologies, to help decrease the environmental effects of mining. With the need for more environmentally effective and clean mining technologies, some gravity separation systems have provided eco-efficient mineral processing solutions in places where it is not otherwise viable in India because of lack of fresh water or for other environmental reason. Advanced spiral separation technologies have offered a cost effective and environmentally viable way to process minerals in India. Recent projects to process mineral sands in the state of Tamil Nadu India have been viable thanks to the use of spiral separators processes using sea water. This paper explores some recent projects where these technologies made the projects environmentally viable. Most of the metallurgical data and findings contained in this paper come from working closely with V.V. Mineral, one of our main clients in the state of Tamil Nadu, and India's largest miner, manufacturer and exporter of Garnet & Ilmenite. For a number of years, Mineral Technologies has closely worked with VV Minerals to provide mineral processing solutions at their different facilities located in Tamil Nadu India. Water issues for mining in India Water shortages are a serious problem for mining companies in India. In a recent survey of India s water situation, Fred Pearce reported that the 21 million wells drilled in recent years are lowering water tables in most parts of the country. From 1947 to 2002, average annual per capita water availability declined by almost 70% to 1,822 cubic meters. Tamil Nadu, located in the southeast tip of India and where we have focused the findings for this paper, is a water-scarce state with a vast mining potential. In addition to mineral sands, the state has diverse potential of minerals such as limestone, lignite, granite, clay, gypsum, feldspar, graphite, and iron. Small quantities of gold, copper, kaolin, bauxite, and asbestos are also available. Even though Tamil Nadu has 33 river basins, the rivers are short, and carry water seasonally making most of these mining projects unviable. In addition to this, the state has a population of more than 62 million people, wells have been drying up at a rampant rate and falling water tables have dried up 95 per cent of the wells owned by small farmers thus reducing the irrigated area in the state by half over the last decade. In communities where underground water sources have dried up entirely, all agriculture is rain-fed and drinking water is trucked in.

5 Mineral Sands deposits in Tamil Nadu - India Heavy mineral sand deposits consist of sand accumulations that contain significant amounts of heavy minerals (generally defined as minerals with a specific gravity greater than 2.8SG). Contained heavy minerals occur as disseminated, associated or concentrated deposits within the sands and often include titanium minerals, zircon, garnet and sillimanite. In India, exploration for, and extraction and processing of heavy mineral sands has intensified in recent years due to increasing use and demand for titanium oxides, metals and alloys. Zircon formerly viewed as a by product has now been a target in light of strong markets, especially China during the years of strong construction growth. The coastal districts of Kanyakumari, Tirunelveli, Thoothukkudi, Nagapattinam and Ramanathapuram in Tamil Nadu are endowed with high quality heavy mineral placers such as Garnet, Ilmenite, Rutile, Leucoxene, Monazite and Zircon. They have wide use in pigment, refractory, ceramic industries and nuclear industry world wide. The Department of Geology and Mining of the Government of Tamil Nadu,estimates reserves of these deposits at about 23 million tonnes of Garnet, 98 million tonnes of Ilmenite, 5 million tonnes of Rutile, 2 million tonnes of Monazite and 8 million tonnes of Zircon. The major players are the Indian Rare Earths (IRE), a Government of India Undertaking, V.V. Minerals, Beach Mineral Company, Transworld Garnet and Indian Ocean Garnet Sand. Mineral Sands processing with spirals in Tamil Nadu India Gravity concentration of minerals in India has traditionally been recognized as a low cost and environmentally friendly process for the separation of minerals. Spirals separators are simple, low energy consuming devices that separate minerals based on their respective densities and have proven to be metallurgically efficient and cost effective since their widespread commercial introduction more than 60 years ago. Mineral sands processing in Tamil Nadu usually consists of wet and dry processes to extract mineral concentrates. A typical wet plant will consist of pumping, hydrocyclones for desliming, surge bins, spirals, up current classifiers and wet magnetic separation (Figure 1) Wet plants in India are usually fed with water directly sourced from the sea with pumps located near the coast line (Figure 2).

6 Process water ponds which handle sea water are specially lined with concrete ensuring the sea water doesn t infiltrate the ground. Spiral tailings are treated through hydrocyclones and the overflow water recovered and sent to tailing ponds. Only 5-10% of the process plant water reports with the final HMC and tailings which are again handled in concrete lined ponds. Water overflow is recovered and sent back to the process water ponds. In the case of VV Mineral they operate 8 spiral separation plants (Figure 3) which stretch from Kanyakumari to Tuticorin near the coastline of Tamil Nadu. Total spiral plant processing capacity at VV Minerals operations is 1,180tph made up of eight plants with feed rates varying from 40 tph to 500 tph as detailed below: Three 120 tonnes per hour feed plant One 40 tonne per hour feed plant One 50 tonne per hour feed plant One 80 tonne per hour feed plant One 150 tonne per hour feed plant One 500 tonne per hour feed plant Sea water vs. fresh water spiral performance A series of tests to determine the variance in spiral performance when operated with either fresh water or sea water were carried out at VV Minerals operations over a two month period. The trials utilized MG6.3 and HG10 spiral separators. A series of 8 tests were carried out on the two spiral models at feed rates varying between 1.2 to 2.1 tph. Pulp density fed to the spirals varied within the range of 35.7% and 41.7% solids (w/w). As the tests were carried out in an operating plant environment there were inevitable variations in the feed conditions throughout the tests. In some tests the spirals were operated at higher feed rates on the salt water slurry. In the case of the HG10, the spiral was operated at 2.0 t/h on fresh water whereas it was run at 2.4 t/h on salt water. This is a 20% increase, which is significant. In the case of the MG6.3, the feed rate was 2.7 t/h on fresh water and 11% higher at 3.0 t/h on sea water. Overall there was no conclusive difference in performance between salt water and fresh water processing on the MG6.3 and HG10 spirals (once variations in feed conditions were taken into

7 account) (figure 4). While this result is perhaps not surprising given that there is very little difference in viscosity or specific gravity between salt water and fresh water it does further reinforce the viability of using low quality water in spiral separation plants. The use of sea water, or highly saline water, will naturally increase the potential for corrosion in and around the processing plant and may reduce the life of the plant if a high level of corrosion protection is not maintained. Spiral separators however are manufactured from fibreglass with a highly resistant polyurethane surface and are far less susceptible to corrosive attack in such environments. Fresh water savings in the spiral plants at VV Mineral The average water requirement for a spiral plant is between tph of water per tonne of solids feed. The total spiral plant capacity at VV Mineral is 1,180 tph for the 8 plants currently in operation. Taking this into consideration and with the use of sea water in their process, fresh water savings at VV Minerals run in the order of 4,248,000 litres per day. According to the Stockholm International Water Institute, 100 litres a day is the minimum per capita water requirement for India s basic domestic needs. With this in mind VV Mineral s fresh water savings provide an availability of fresh water per day for 42,480 people in the Tamil Nadu State. In addition to this, the use of sea water in these plants has allowed for the viability of these projects that generate employment for local workers in the order of 3,400 direct employments High Capacity spirals (HC Spirals) Ongoing research and development efforts have improved separation efficiencies of spiral models over the years. Improvements in materials of manufacture have reduced weight and enhanced operational capabilities. The concept of a high capacity, small footprint processing plant has now been successfully commercialized in recent mineral sands and iron ore projects. In some cases a small footprint, high capacity plant was necessary to make projects viable. Modern high capacity spiral models can process up to 35 tph per quad start spiral. In some cases both the rougher and scavenger processing stages are incorporated into the same spiral. Conventional spiral separators can process up to 9 tph per triple start spiral.

8 Combining rougher and scavenger stages of separation into one unit obviates the need for intermediary equipment including feed sumps, pumps and motors, electrics, laundering and feed distribution systems. The introduction of two stage high capacity spirals into the industry has allowed the reduction of plant foot prints to just 40% of the area of plants designed based on conventional (i.e.: low capacity) spiral technology (Figure 5). This provides substantial environmental and capital cost savings in the plant construction costs and Results in an efficient, non-polluting and low energy solution for concentrating heavy minerals. CONCLUSIONS With the need for more environmentally effective mining technologies, spiral separation technologies have been shown to provide eco-efficient mineral processing solutions in India and places where wet processing is not otherwise viable because of a lack of fresh water. Tests carried out in operations in Tamil Nadu, India, show no substantial difference in metallurgical performance of spiral separators when treating slurries based on either salt water or fresh water. This has allowed for the viability of these projects that generate not only employment for local workers (3,400 direct employments) but vast fresh water savings for communities in this water scarce region (savings in excess of 4 million litres of water per day). The focus in spiral plant design in recent years has been to not only improve separation efficiencies, but to significantly increase feed capacities and look more broadly at ways of optimizing the overall process design rather than just individual separation stages. A recent success of this focus is the concept of a high capacity, low footprint spiral processing plants that enable plants to be constructed and operated using less steel and pumping power than previously possible. ACKNOWLEDGEMENTS I will like to acknowledge the assistance of VV Minerals in India that allowed testing of spiral equipment in their Tamil Nadu operations and to the staff at Mineral Technologies for their valuable guidance and assistance with a special thanks to Mark Palmer. I also thank the management of Mineral Technologies for permission to publish this paper. REFERENCES

9 Business Monitor International, 2009, India Mining Report Q including 5-year industry forecasts. Mermaid House London, UK Government of Tamil Nadu, Department of Geology and Mining. An overview of mineral reserves (2006). Available from: [Accessed: 03/October/2009]. Lester Brown, 2007, Earth Policy Institute, Water shortages in India Report, Washington USA Pearce, F, 2007 When the Rivers Run Dry: Water--The Defining Crisis of the Twenty-first Century p Beacon Press, Boston MA USA The Stockholm International Water Institute (2006) Statistics [Accessed: 03/October/2009] Mark Palmer, 2007, High Capacity Gravity Separation Solutions, Industrial Minerals a Metals Bulletin Publication. London UK FIGURE CAPTIONS Fig 1 - Typical wet plant with spiral circuit in mineral sands operations Fig 2 - Sea water pump for wet spiral concentration plants Fig 3 - Sea water spirals at VV Mineral Fig 4 - Sea water vs. fresh water spiral tests data and performance curves Fig 5 - Reduce Plant Foot Print with HC Spirals

10 Scavenger Primary Middling 2 From MUP 40 Re-Cleaner LIMS Cleaner 33 Linear Screen 76 Non-Mags 81 Static Screen 6 Primary WHIMS Cyclone Banks TK006 TK007 TK008 Non-Mags TK005 TK010 TK Dewatering TK TK012 Non-Mags Dewatering TK TK003 Overflow Scavenger Key 81 Non-Mags Stockpile TK011 Secondary WHIMS Upstream Classifier Stacker Grade (%HM) Mags TK014 Fig 1 - Typical wet plant with spiral circuit in mineral sands operations 86 Non-Mags

11 Fig 2 - Sea water pump for wet spiral concentration plants Fig 3 - Sea water spirals at VV Mineral

12 Test 1, HG10, Sea Water, 1.58 t/h, 40.1% solids, 73.53% HM Stream Flow rates Chemical Analysis Cumulative Separation Solid Kg/hr Water Mass Shell HM LM HM Mass HM Efficiency Kg/hr Dist'n% Recovery Dist% recovery% % Con Mid Tail calc. feed meas. Feed Test 2, HG10, Fresh Water, 1.20 t/h, 37.8% solids, 71.13% HM Stream Flow rates Chemical Analysis Cumulative Separation Solid Water Mass Shell HM LM HM Mass HM Efficiency Kg/hr Kg/hr Dist'n% Recovery Dist% recovery% % Con Mid Tail calc. feed meas. Feed Test 3, MG6.3, Sea Water, 1.66 t/h, 35.7% solids, 21.08% HM Stream Flow rates Chemical Analysis Cumulative Separation Solid Kg/hr Water Mass Shell HM LM HM Mass HM Efficiency Kg/hr Dist'n% Recovery Dist% recovery% % Con Mid Tail calc. feed meas. Feed Test 4, MG6.3, Fresh Water, 1.48 t/h, 35.8% solids, 22.56% HM Stream Flow rates Chemical Analysis Cumulative Separation Solid Water Mass Shell HM LM HM Mass HM Efficiency Kg/hr Kg/hr Dist'n% Recovery Dist% recovery% % Con Mid Tail calc. feed meas. Feed Sea water vs. fresh water spiral tests 1 to 4

13 100 Spiral Tests - Fresh water versus Sea water 100 Spiral Tests - Fresh water versus Sea water HM Recovery % HM Separation Efficiency % Test 1, HG10, Sea Water, 1.58 t/h, 40.1% solids, 73.53% HM 10 Test 2, HG10, Fresh Water, 1.20 t/h, 37.8% solids, 71.13% HM Cumulative mass yield% Test 1, HG10, Sea Water, 1.58 t/h, 40.1% solids, 73.53% HM 10 Test 2, HG10, Fresh Water, 1.20 t/h, 37.8% solids, 71.13% HM Cumulative mass yield% Sea water vs. fresh water spiral tests 1 and 2 performance curves

14 100 Spiral Tests - Fresh water versus Sea water 100 Spiral Tests - Fresh water versus Sea water HM Recovery % HM Separation Efficiency % Test 3, MG6.3, Sea Water, 1.66 t/h, 35.7% solids, 21.08% HM Test 4, MG6.3, Fresh Water, 1.48 t/h, 35.8% solids, 22.56% HM 10 Test 3, MG6.3, Sea Water, 1.66 t/h, 35.7% solids, 21.08% HM Test 4, MG6.3, Fresh Water, 1.48 t/h, 35.8% solids, 22.56% HM Cumulative mass yield% Cumulative mass yield% Sea water vs. fresh water spiral tests 3 and 4 performance curves

15 Test B1, MG6.3, Fresh Water, 2.10 t/h, 39.8% solids, 34.68% HM Stream Flow rates Chemical Analysis Cumulative Separation Solid Kg/hr Water Mass Shell HM LM HM Mass HM Efficiency Kg/hr Dist'n% Recovery Dist% recovery% % Con Mid Tail calc. feed Test B2, MG6.3, Sea Water, 1. t/h, 40.3% solids, 34.55% HM Stream Flow rates Chemical Analysis Cumulative Separation Solid Water Mass Shell HM LM HM Mass HM Efficiency Kg/hr Kg/hr Dist'n% Recovery Dist% recovery% % Con Mid Tail calc. feed Test B3, HG10, Fresh Water, 1.99 t/h, 41.7% solids, 87.27% HM Stream Flow rates Chemical Analysis Cumulative Separation Solid Kg/hr Water Mass Shell HM LM HM Mass HM Efficiency Kg/hr Dist'n% Recovery Dist% recovery% % Con Mid Tail calc. feed Test B4, HG10, Sea Water, 2.11 t/h, 41.6% solids, 87.45% HM Stream Flow rates Chemical Analysis Cumulative Separation Solid Water Mass Shell HM LM HM Mass HM Efficiency Kg/hr Kg/hr Dist'n% Recovery Dist% recovery% % Con Mid Tail calc. feed Sea water vs. fresh water spiral tests 5 to 8

16 100 Spiral Tests - Fresh water versus Sea water 100 Spiral Tests - Fresh water versus Sea water HM Recovery % HM Separation Efficiency % Test B1, MG6.3, Fresh Water, 2.10 t/h, 39.8% solids, 34.68% HM 10 Test B2, MG6.3, Sea Water, 1. t/h, 40.3% solids, 34.55% HM Cumulative mass yield% 10 Test B1, MG6.3, Fresh Water, 2.10 t/h, 39.8% solids, 34.68% HM Test B2, MG6.3, Sea Water, 1. t/h, 40.3% solids, 34.55% HM Cumulative mass yield% Sea water vs. fresh water spiral tests B1 and B2 performance curves

17 100 Spiral Tests - Fresh water versus Sea water 100 Spiral Tests - Fresh water versus Sea water HM Recovery % HM Separation Efficiency % Test B3, HG10, Fresh Water, 1.99 t/h, 41.7% solids, 87.27% HM Test B4, HG10, Sea Water, 2.11 t/h, 41.6% solids, 87.45% HM 10 Test B3, HG10, Fresh Water, 1.99 t/h, 41.7% solids, 87.27% HM Test B4, HG10, Sea Water, 2.11 t/h, 41.6% solids, 87.45% HM Cumulative mass yield% Cumulative mass yield% Sea water vs. fresh water spiral tests B3 and B4 performance curves Fig 4 - Sea water vs. fresh water spiral tests data and performance curves

18 Fig 5 - Reduce Plant Foot Print with HC Spirals